1. Field of the Invention
The present invention relates to a wireless communication system.
2. Description of the Related Art
Generally, a transceiver for a 3rd Generation (3G) and/or a 4th Generation (4G) mobile communication system controls transmission and reception operations on a per-frame basis. For example, in the Long Term Evolution (LTE) standard, which is one of the 4 G communication standards, one frame has a length of 10 milliseconds (ms), and includes 10 subframes, each having a length of 1 ms.
A receiver controls a communication channel on a per-subframe basis, and programs operations of a respective mobile communications system. A transmitter also controls the channel on the per-subframe basis, and programs operations of a respective mobile communications system. At this time, the transmitter may execute a Discontinuous Transmission (DTX) mode so as to intermittently turn on/off an output in a subframe period. The DTX mode saves power consumption in a transmitter. For the same purpose, the receiver may execute a Discontinuous Reception (DRX) mode. The main roles of the DTX mode and the DRX mode are to allow a terminal not to continuously monitor control channels, and to deactivate a Radio Frequency (RF) block, thus placing it into a sleep state, and to immediately activate the RF block in a defined interval. An example of an RF output dependent on the DTX mode is illustrated in FIG. 1 below.
FIG. 1 illustrates RF outputs that depend on a DTX mode in a wireless communication system according to the related art.
Referring to FIG. 1, a frame 110 includes a plurality of subframes 120. In FIG. 1, the DTX mode is defined as turning on a transmission operation at an even-number subframe and turning off the transmission operation at an odd-number subframe. According to this, as illustrated in FIG. 1, the RF outputs occur in the even-number subframes, and do not occur in the odd-number subframes. For example, the LTE standard prescribes that a time required for completing a transition from a shut-down state to an activation state or from the activation state to the shut-down state, according to the DTX mode, be within 20 microseconds (μs).
Generally, a transmitter of a wireless communication system includes a RF Integrated Circuit (RFIC), a Power Amplifier (PA), and a front end. In a 2nd Generation (2G) system, a 2.5 Generation (2.5G) system, and other similar systems, the RFIC, the PA, the front end, and other similar elements, were directly supplied with a battery power as their power sources for operation. The PA is an element typically having the highest power consumption in the transmitter. When the PA is directly supplied with the battery power, the loss characteristics of the PA may vary according to a change of voltage resulting from charging and/or discharging of a battery. Accordingly, until the depletion of charged battery cells occurs after the charging of the battery cells, or in other words, during a discharging of the battery cells, the efficiency characteristics of the PA are not at an optimal point. That is, the PA fails to maintain excellent characteristics over the whole interval including the charging and the discharging of the battery cells. Also, in a geographic area crowded with base stations, such as a metropolitan area, a transmission output of the PA may be low power or mid power rather than peak power. But, at the time of low power or mid power transmission output, a PA that is optimized for efficiency at peak power using the battery voltage may suffer a big loss because of an unnecessarily high source voltage.
According to this, in order to eliminate a factor of performance loss resulting from a battery voltage change or a mid power transmission, a next-generation communication system employs a voltage regulator, such as a Direct Current (DC)-DC converter, a Low Drop-Out (LDO) linear regulator, and other similar or suitable voltage regulators, in order to regulate battery power, and supplies a pre-regulated power source as power sources for core devices of a transmitter. Due to this, although there is a change of voltage during a charge/discharge cycle of the battery, the transmitter may be supplied with a regulated voltage that is regulated through the voltage regulator and, even for low power or mid power transmissions, the transmitter may also be supplied with a power source having as low voltage as necessary. Accordingly, the core devices of the transmitter may continuously operate at an optimal efficiency point and also, a power loss resulting from a source voltage overhead may be prevented.
The voltage regulator supplying the regulated voltage may include a capacitor having a very large capacity at its output port, and may regulate an output voltage using the capacitor. Accordingly, quite a long time may be needed in order to make a transition from an off state to an on state and reach a regulated voltage, or in order to make a transition from the on state to the off state and reach 0V. That is, the time required for the charge/discharge cycle of the capacitor makes it impossible to turn on/off the voltage regulator according to an activation/deactivation cycle of a transmission operation dependent on very fast time intervals, such as the DTX mode.
As described above, if a communication device is powered up, the voltage regulator may maintain an on state regardless of on/off of devices in the transmitter. Due to this, the voltage regulator consumes a current used for operation, even in an idle state, in which the transmitter does not operate. Generally, for a relatively long time, a mobile terminal operates in the idle state so as to be not transmitting and receiving, such that electric current that the voltage regulator continuously consumes during the idle state may reach a considerable amount as an accumulated power loss. Also, the voltage regulator continuously consumes electric current, even in the DTX mode described with reference to FIG. 1. This problem may also occur even in the DRX mode. According to intuitive recognition, it seems that the power waste problem of the voltage regulator may be addressed if the amount of current consumed by the voltage regulator is designed to be small. But, decreasing the amount of current consumed may incur a new problem of causing a deterioration of performance. Accordingly, there is a need to propose an alternative for minimizing the amount of current consumed by the voltage regulator without performance loss due to the voltage regulator.